Control apparatus



May 15, 1962 E. A. wAcHsMUTH CONTROL APPARATUS 2 Sheets-Sheet 1 Filed NOV. 18, 1957 FIG. 12.

INVENTORZ FIG. 1.

ATTORNEY May 15, 1962 E. A. wAcHsMUTH CONTROL APPARATUS 2 Sheets-Sheet 2 Filed Nov. 18, 19574 INVENTOR: BY ERICH A. WACHSMUTH www ATTORNEY United States Patent 3,034,441 CONTROL APPARATUS Erich A. Wachsmuth, Michigan City, Ind., assigner to .Icy Manufacturing Company, Pittsburgh, Pa., a corporation of Pennsylvania Filed Nov. 18, 1957, Ser. No. 697,012 16 Claims. (Cl. 10S- 41) is more particularly suited for a counterstroke type of free piston compressor as has been more fully shown, described and claimed in my copending application entitled Starting and Regulating Apparatus for Free-Piston Compressors, Serial No. 634,395, tiled January 2, 1957, now Patent No. 2,841,322. Although the control apparatus described in the above-identified copending application has excellent performance characteristics, under certain operating conditions it is desirable to obtain different control characteristics which are obtainable by the hereinafter described novel control apparatus.

Accordingly one object of my invention is to provide new and improved apparatus for hydraulically controlling the cylinder unloaders of a compressor.

Another object of my invention is to provide new and improved apparatus for controlling the cylinder unloaders of a compressor to obtain rapid return of the unloader to a position allowing the compressor suction Valves to be closed.

A more specific object of my invention is to provide new and improved apparatus for controlling the cylinder unloaders of an air compressor having a pair of spaced hydraulic passageways in each of which suitable valve means are disposed which function in an alternative manner.

Another more specific object of my invention is to provide new and improved apparatus for controlling the cylinder unloaders of a compressor comprising a pair of spaced hydraulic passageways in which oppositely biased valves are disposed, respectively.

A particularly important object of my invention is to provide new and improved apparatus for controlling the cylinder unloaders of a free piston type of compressor so that the quantity of medium delivered by the compressor is substantially equal to the demand at all times.

A more specific object of my invention is to provide new and improved apparatus for controlling the cylinder unloaders of a counterstroke free piston type of compressor which employs a means for removing the actuating force from the unloader, the operation of which varies with relation to the pressure of the receiver to which the compressor discharges.

Still another more specific object of my invention is to provide new and improved apparatus for controlling the cylinder unloaders of a compressor which employs a helical control edge in conjunction with an elongated arcuate port to relieve the actuating force from the unloader, the operation of which varies with relation to the pressure of the receiver to which the compressor discharges.

These and other objects of my invention will become more apparent when taken in conjunction with the following detailed description of a preferred embodiment thereof and the following drawings in which:

FIGURE l is a partial side elevational and partial longitudinal cross sectional view of control apparatus constructed in accordance with the principles of my invention, the mechanism for obtaining the operation thereof, and the unloaded devices actuated thereby;

FIGURE 2 is an enlarged cross sectional view of a portion of the control apparatus as shown in FIGURE l with the plunger thereof being shown in a position prior to its compression stroke;

FIGURE 3 is similar to the cross sectional view as shown in FIGURE 2 with the plunger thereof shown in a position slightly in advance of the fluid entry ports;

FIGURE 4 is similar to the cross sectional view as shown in FIGURE 2 with the plunger thereof shown during its return stroke;

FIGURE 5 is a cross sectional view of the control apparatus as shown in FIGURE 2 taken substantially along the lines V-V thereof;

FIGURE 6 is a cross sectional view of the control apparatus as shown in FIGURE 5 taken substantially along the lines VI-VI thereof;

FIGURE 7 is a cross sectional view of the control apparatus as shown in FIGURE 8 taken substantially along the lines VII-VII thereof; 4

FIGURE 8 is a cross sectional view of the control apparatus as shown in FIGURE 2 taken substantially along the lines VIII-VIII thereof;

FIGURE 9 is a cross sectional view of the control apparatus `as shown in FIGURE 2 taken substantially along the lines IX-IX thereof;

FIGURE l0 is a cross sectional view of the control apparatus as shown in FIGURE 2 taken substantially along the lines X-X thereof;

FIGURE ll is a cross sectional view of the control apparatus as shown in FIGURE 7 taken substantially along the lines Xl--XI thereof;

FIGURE l2 is a diagrammatic representation of the cylinder pressure-piston stroke relationship in one cylinder of a compressor employing a cylinder unloader control apparatus constructed in accordance with the principles of my invention and in addition shows the displacement of the unloaders and the pressure in the system connecting the unloader control apparatus with the unloaders with reference to the piston stroke.

Referring to FIGURES l and 2 of the drawings it will be noted that a control device constructed in accordance with the principles of my invention comprises a suitable elongated hollow housing 2 in which an elongated formed cylindrical plunger 4 is mounted for reciprocable movement therein. The inner end of the housing 2 may be secured to a suitable frame 17 of a compressor in any suitable manner whereby reciprocating movement of the plunger 4 is obtained by means of a suitable follower mechanism 8 which extends inwardly of the housing 2 from the open inner end thereof into engagement with the inner end of the plunger 4. The follower mechanism v8 includes an oscillating cam -10 mounted on an oscillating shaft -12 as is known in the art. In order to insure engagement between the plungerl 4 and the follower mechanism 8 a spring 14 is suitably secured to the plunger 4 and reacts against the housing 2 so as to normally bias the plunger 4 outwardly of the inner end of the housing 2. The plunger 4 is rotatable about its longitudinal axis by means of a suitable gear 16 which engages a rack (not shown) whereby the relative angular position of the plunger 4 in the housing 2 may be varied. It is particularly to the borne in mind that the above structure and its operation, other than that of the housing 2 and the plunger 4 as hereinafter described, has particularly been shown, described and claimed in the aboveidentified application; and, accordingly, for a more comprehensive description thereof the above-identiiied application should be referred to. Further, although the principles of my invention are equally applicable to many types of compressors for various mediums, for the purpose of better understanding my invention an air compressor is referred to hereinafter. It is to be understood, however, that such reference to an air compressor does not limit the application o my new and improved control apparatus to an air compressor.

Referring to FIGURES 2, 3 and 4, it will be noted V that rthe housing `2 is provided with an approximately central inwardly extending ring and that the outer end of the housing 2 is laterally reduced in cross section to provide a fluid reservoir 22 between the outer end of the housing 2 and the ring 20. A suitable hydraulic fitting (not shown) is secured to the housing to connect the reservoir 22 to a suitable supply (not sho-wn) of hydraulic iiuid in any suitable manner as is well known in the art. yAs hereinafter described'various components are located within the central opening of the housing 2 in fixed relationship, however, the use of such separate components is only for the purpose of permitting the formation of the various structural features of the control device as hereinafter described. From a structural standpoint the various components of the housing 2 may be vformed integral with the housing 2, or, if feasible, the structures of' various components may be combined into a single component.

As shown, a formed elongated tubularV barrel 26 is centrally located withinV the housing 2 which has a central elongated bore of a diameter to slidably receive the outer portion of the plunger 4 therein. The inner longitudinally extending portion of the barrel 26 is radially Vreduced in size to provide an integral radially outwardly extending shoulder 28 intermediate the ends of the barrel 26. In addition the outer surface of the barrel 26 is provided with an undercut portion which extends axiallyV outwardly from the shoulder 28 and in which an elongated tubular sleeve 30 is closely received. As will become apparent theV sleeve 30 has an outside diameter i substantially the same as the outside diameter ofthe enlarged outer portion of the barrel 26 to permit the sleeve 30 to be located on the barrel 26 and the entire assembly then inserted through the reduced cross section of the outer end of the housing 2V. The sleeve 30 is provided to facilitate the forming of passageways within the barrel 26 as hereinafter described and after the formation thereof the sleeve 30 is preferably rigidly secured to the barrel 26 in any suitable manner such as by being copper soldered thereto. In order to support the outer end of the barrel 26 within the housing 2, the outer end thereof is received within the inner end of the reduced cross section outer end of the housing 2. As shown, the ring 20 is provided with an annular recess 24 extending 'radially outward from its inner end with its open side facing the outer end of the housing 2 for the purpose yof receivingV the shoulder 28 of the barrel 26 and the inner end of the sleeve 30 therein whereby the barrel 26 and sleeve -30 are held radially and longitudinally in position within the housing 2.

As shown'fa cylindrical valve block 32 is closely received within the reduced outer end portion of the housing 2 with its inner end abutting the outer end of the barrel 26.V -A cylindrical passageway block 34 is also closely received within the reduced outer portion of the housing y2 with its inner end abutting the outer end of the valve block 32. A suitable hydraulic line 36 is next located within the reduced outer port-ion of the housing 2 with its inner end abutting the outer end of the passageway block 34. The line 36 (see FIG. l) is held in hydraulic relationship with the block 34 by means of asuitable hydraulic fitting assembly 38 as is well known in the art. Although the structure of the line 3.6 and the hydraulic tting assembly 38 may be of any suitable construction as is well known in the art, the fitting assembly 38 preferably extends inwardly of the reduced outer portionof the housing 2 and encircles the line 36. As shown a suitable gasket is provided inwardly of the hydraulic -iitting assembly 38 to prevent leakage of hydraulic tiuid from the outer end of the housing 2. Although not described, it is to be realized that if desired various interlocking means may be employed between the components described to insure'their proper operating alignment at all times. The other end of the line 36 is connected to a suitable hydraulically operated cylinder unloader 7 which is movable to control the operation of a compressor suction valve 9 as is more particularly described in the above-identified application.

One particularly novel structure of my invention resides in the valve block 32 which has a pair of spaced hydraulic passageways extending therethrough `and in each of which suitable valve means is provided to control the iiow of hydraulic fluid therethrough. Thus as shown the valve -block 32 is provided with a hydraulic passageway 40 which extends axially from the outer end of the bore in the barrel 26 to approximately the mid-point of the valve block 32. The passageway 46 extends into a radially enlarged hydraulic passageway 42 which extends axially from the passageway 40 to the outer end of thervalve -block 32. A check valve 44 is located within the passageway 42 which is of any suitable construction so `as'tobe operable to hydraulically open and close the passageway 40 depending upon the hydraulic pressure therein. As shown the valve 44 comprises a slidable hollow sleeve 45 having a generally conical end 46 which is normally biased by means of an internally located coil spring 47 into engagement with a seat 48 on the outer end of the hydraulic passageway 407 to prevent hydraulic fluid from iiowing t through the passageway 42. The valve block 32 is provided with another hydraulic passageway 50 which extendsy -axially from the outer end of the bore of the barrel 26 and which terminates inwardly of the outer end of the valve block 32.l The passageway 50 extends into a radially restricted hydraulic passageway 52 .which extends axially from the outer end of the passageway 50 to the outer end of the valve block 32. A suitable plunger valve 54 is located in the hydraulic passageway 50 which is axially slidable therein to hydraulically block the passageway 52. IIf desired, in order to facilitate the producing of the block 32 the passageway 52 may be formed in a sleeve 53 lwhich is pressed intothe outer end of the passageway 50. The plunger valve 5'4 is biased outwardly from the barrel 26 by means of an internally located coil spring 51 which extends between the outer end of the barrel 26 and the outer end of the recess in the plunger valve 54 in which it is located.

As indicated, the line 36 and the passageway block 34 are disposed in abutting relationship and when so located provide a Y-shaped hydraulic passageway 56 with the arms thereof being connected to the passageways 52 and 42 whereby the passageways 52 and 42 are hydraulically connected to the line 36 through the iitting assembly 38. =It will also be noted that the passageway 50 is radially enlarged at the outer end to provide a chamber 58, which chamber 58 (see also FIG. 6) is hydraulically connected by lmeans of a hydraulic passageway 60 which extends axially and radially inwardly of the block 32. The passageway `60 terminates into a semi-circular hydraulic passageway 62 which extends inwardly of the valve block 32 from the inner end surface of the valve mock sz. Referring to FIGURE 7, it win -be noted that the sidewall of the barrel 26 is provided with a pair of diametrically spaced axially extending hydraulic passageways 64, the innermost ends'of which extend radially inwardly of the barrel 26. In order to accomplish the purposes of my invention the intersection of the passageways 64 with the running surface of the barrel 26 are of an elongated, arcuate shape to form control ports 65 in the running surface of the barrel 26, for a purpose as more fully described hereinafter. The passageways 64 are spaced within the barrel 26 to avoid other passageways therein as hereinafter described and have their outer ends hydraulically connected to the opposite ends of the passageway 62 so as to be responsive to the pressure in the chamber 58. If desired, a single passageway 64 may be employed in conjunction with a single control port 65. A pair of diametrically spaced passageways 64 are preferably employed to exert the same hydraulic force on opposite sides of the plunger 4. It will also be noted (FIG. 7) that the portion of the passageways 64 extending into the running surface of the barrel 26 are located under the sleeve 30 to facilitate their fabrication.

The barrel 26 is provided with a pair of radially outwardly extending ports 66 adjacent its outer end which extend lbetween the running surface thereof and the reservoir 22 in the housing 2 to permit hydraulic uid to enter the bore between the plunger 4 and the valve block 32. In addition the barrel 26 (FIGS. 8 and 9) is provided with a pair of radially outwardly extending hydraulic passageways 68 which also extend through the portions of the sleeve 30 in alignment therewith whereby the running surface of the barrel 26 is connected to the reservoir 22 at a point spaced longitudinally inwardly of the ports 66. The passageways 68 are arcuately displaced from the passageways 64 for purposes as more fully described hereinafter.

The plunger 4 is provided with a head portion 70 which is of a size to be closely received within the bore so as to compress hydraulic uid therein as is well knolwn in the The head 70 is ofa length less than the distance between the ports 66 and the passageways 68 as will become apparent hereinafter. As more fully described in the above-identified copending application the plunger 4 is reciprocable within the bore of the barrel 26 so that the head 70 is moved lfrom an inner position located longitudinally inwardly from the'supply ports 66 (FiG. 2) to an outer position whereat it is spaced slightly inwardly from the inner surface of the valve block 32. An annular relief space 72 is provided longitudinally inwardly of the head 70 about the outer surface of the plunger 4. In addition, the outer surface of the plunger 4 is provided with a pair of longitudinally inwardly extending, diametrically spaced, arcuate, vwedge shaped segments 73 having their base portion connected to the relief space 72. Such a construction provides a pair of diametrically spaced helical control edges 74 on the outer surface circumference of the plunger 4 which are cooperable with the control ports 65, respectively, in a manner as described hereinafter to vary the period of opening of the control ports 65.

The operation of my control device may readily be understood by referring to FIGURE l2 and by considering the plunger 4 as being initially located as it starts its outward movement, as shown in FIGURE 2. At this initial starting point identified as O, the plunger 4 starts traveling outwardly, toward the valve block 32 displacing through ports 66 the hydraulic fluid in front of the head portion 70 into the reservoir 22 which surrounds the upper part of the barrel 26. As such outward movement continues the straight control edge at the outer end of the head 70 of the plunger 4 closes the ports 66 to entrap hydraulic fluid within the pumping chamber formed by the bore of the barrel 26 between the head portion 70 of the plunger 4 and the block 32. After the ports 66 have been closed further outward movement of the plunger 4 causes the pressure to build up rapidly in the pumping chamber until a pressure is achieved to cause the normally closed spring biased check valve 44 to open. The pressure-stroke relationship in the line 36 during this period is represented by the straight line O-A, which is at the pressure of the hydraulic supply system. During this time the outwardly biased plunger valve 54 continues to be located to close the connection between the line 36 and the chamber 58 (see FIG. 3). With further outward movement of the plunger 4, after the actuating pressure of the check valve 44 has been achieved, the pressure in the line 36 builds up rapidly until it reaches the actuating pressure of the cylinder unloader 7 connected thereto. The pressure-stroke relationship during this period is represented by the line A-B which, in addition to extending upwardly, also is inclined outwardly along the X-axis. Such inclination is primarily due to the elasticity of the pumped liuid and the pressure system itself. During the period the pressure within the control system remains at atmospheric pressure (O-A) and rapidly increases (A-B) the unloader 7 remains in a normal unactuated position (line O'-R) due to the fact that the actuating pressure thereof has not been achieved. After the actuating pressure of the unloader has been reached, the unloader makes its full lift, which is limited by mechanical means, as is well known in the art, while the pressure rises only moderately due to the displacement effect of the unloader 7. The pressure-stroke relationship during this period is represented by the upwardly and outwardly extending line B-C and the lift of the unloader 7 is represented by the line R-S. When the unloader 7 stops its lift movement at a point which corresponds to point C of the pressure diagram, the pressure in the system rises again whereby the peak pressure is reached, which is determined by the Volume displaced by plunger 4 within the remaining period of the outward stroke of the plunger 4. Again the total volume of fluid in the pressure system, the modulus of elasticity of the fluid and the elasticity of the pressure system itseif, will effect the pressure stroke diagram of this system. The pressure-stroke relationship during the period is represented by the line C-D which extends sharply upwardly and somewhat outwardly along the X-axis. As the lift of the unloader 7 is limited by suitable means the lift remains the same for so long as the required actuating force is applied thereto. As indicated diagrammatically and as described in the above-identified copending application the compression or outward stroke of the plunger 4 is coordinated to the suction stroke of the cornpressor.

At the moment plunger 4 starts its inward stroke at point D, the pressure in the pumping chamber breaks down causing the force of the spring 47 to close the check valve 44 and the plunger valve 54 to open the connection between the line 36 and the chamber 58 due to the higher pressure extended by the hydraulic fluid against the outer end of the plunger valve 54 which is suicient to overcome the bias of the spring 51. As has been described the chamber S8 is hydraulically connected by means of passageways 6l), 62 and 64 to the ports 65 in the running surface of the bore of the barrel 26. In order to facilitate the flow of fluid to passageway 60, the outer end of the plunger valve 54 may be reduced to provide a larger fluid passageway within the chamber 58. The ports 65 extend angularly therein with reference to the longitudinal axis of the barrel 26, so as to vary the opening of the ports 65. Inasmuch as such ports 65 and rotatable helical control edges 74 are well known in the art further description thereof is not believed to be necessary. The above identified copending application also contains a more particular description of the cooperation of such structure. For the purpose of illustrating the relative position of the ports 65 of the passageways 64 and the control edges 74, the control edges 74 and ports 65 remote from the side from which FIGURES 2, 3, and 4 are taken have been shown in dotted outline. Although not shown it will be obvious that the longitudinal axes of the ports 65 extend in directions which are displaced from each other so as to be cooperable with the respective control edges 74 which are displaced 180 from each other as heretofore indicated. By such structure each control edge 74 has the identical effect on the control port 65 cooperable therewith as the plunger 4 is rotated around its longitudinal axis. Thus, during the inward stroke of the plunger 4, the chamber 58 is selectably connected to a pair of control ports 65 in the running surface of barrel 26. The control ports 65 of the passageways 64 are controlled by the helical control edges 74, respectively, of plunger 4, in such a manner that the ports 65 become opened sooner or later, depending upon the angular displacement of the plunger 4. The pressure-stroke relationship from the period the plunger 4 starts its inward movement until the ports 65 are opened is represented initially by the line D-E. In view of the fact Ithat the time required for the opening of the ports 65 may be varied it is to be realized that the location of point E, and consequently, the length of line D-E may vary. As indicated E represents a partial load condition of an air cornpressor during which it is desired to reduce the cubic feet of compressed air delivered by the compressor; accordingly, the cylinder unloader 7 holds the suction valve 9 open only for a portion of the compression stroke of the air compressor as is well known in the art.

As described in the above-identiiied copending application such angular displacement Yof the plungerY 4 is controlled by the receiver pressure so that the length of time the unloader 7 holds the suction valve 9 open, and, consequently, the quantity of air delivered by the compressor is proportional to the receiver pressure, that is, the demand for the compressed air. As long as the receiver pressure is less than the low limit desired the angular position of the plunger is such that ports 65 become opened as soon as the plunger 4 starts its return stroke so that the unloader 7 immediately permits the suction valve 9 to close and the greatest amount of compressed air is delivered by the compressor. -For receiver pressures between the desired low limit and the desired high limit, the plunger 4 becomes gradually rotated to such an extent that with rising receiver pressure ports 65 become opened by control edges 74 later and later, causing the unloader 7 to hold the suction valve 9 yopen with rising pressure for an increasing portion of the compressor stroke so that less and less compressed air is delivered by the compressor. The fact that the ports 65 are opened naturally also for a longer or shorter portion of the plunger outward stroke does not iniluence the control device as the connection between the ports 65 and the line 36 is interrupted during the outward compression stroke of the plunger by the closed plunger valve 54. When the ports 65 are. opened when the plunger 4 is traveling inwardly the line 36 becomes immediately connected to the reservoir 22 by the hydraulic connection comprising the passageways 56, 52, 60, 62, 64, ports 65, segments 73 and relief space 72 on the plunger 4, and the passageways 68which are continually connected with the reservoir 22 to cause an immediate breakdown of the pressure in the line 36.

Thus the line D-E represents the holding period for the cylinder unloader 7 of the lair compressor while the plunger 4 is making its inward stroke return. The point Erepresents the point where theV pressure breaks down to connect the line 36 to the reservoir 22 as heretofore described. Inasmuch as the capacity of the reservoir 22 and the supply therefor is substantially infinite with reference to the hydraulic uid in the control system the pressure in line 36 breaks down substantially instantaneously to the latmospheric pressure of the reservoir 22 as represented by the line Upon breakdown of the pressure in line 36 the actuatingV force for the unloader 7 Iis, removed andthe suction valve 9 is closed substantially instantaneously. In general, suction valves such as valve 9, employ spring members to obtain such rapid closing, however, if desired, any suitable closing structure may be employed. Thus, the unloader 7 is hydraulically actuated so thatV the suction valve 9 remains open beyond point S to point T which point T corresponds in time relationship with point E. The suction valve 9' will close during the period represented by line T--U which corresponds in time relationship with line E-F due to the decrease in pressure in the line 36. After point U the suction valve 9 remains closed until it opens again at kthe end of the reexpansion of the succeeding compressor suction stroke. Inasmuch as the location of point E changes as determined by the receiver pressure only, it will be obvious that the point F will lalso vary. The small pressure drop between D and E is caused by the small relief eiect to which 4the pressure system is subject at the moment the pressure valve 54 opens. The line P Q (it is to be realized the points O and O' at each end of FIG. l2 represent the same cyclic point) represents the remainder of the inward stroke of the plunger `4 after pressure has broken down in the system due to the passageways 64 being connected to the reservoir 22. As the line D-E indicates =a partial load condition and as the point E may vary, an idle load condition has been shown for the purpose of showing the Variations of the quantity of air which may be delivered by a compressor, in which the point E has been moved to point E. Under an idle load a portion of the line D-E coincides with the line D--E. Point E corresponds to the beginning of the compression stroke of the compressor when idling and thereafter the functioning of the control along line E- F and FO is identical to that previously described with reference to lines E-F and F--O. Similarly the unloader 7 will retain its full lift until point T lwhich corresponds in time relationship to point E'. Thereafter T-U is identical to T--U previously described. VIt is further to be realized that a multiplicity of points between points E and E -may be obtained depending upon the receiver pressure which controls the opening of the ports 65 and ythfat ya multiplicity of lines similar to lines E-F and E--F would then result.

FIGURE 12 also illustrates the momentary pressure in the compressor system from which the compressed air is delivered which is plotted over a full cycle of the air compressor. From this diagram it will be noted that, as is customary with all compressors, a certain clearance volume CL is provided between the outermost end of the stro-ke of the piston and the head of the cylinder of the air compressor. Due to the compressed air in the clearancefvolume, as the piston of the compressor starts its suction stroke a certain re-expansion of the air in the clearance volume CL will occur 'which starts at the dis- Vcharge pressure of the compressor, point H, and follows a generally adiabatic re-expansion to the point I at which time the re-expanded air will be at atmospheric pressure so that additional air may be sucked into the cylinder of the compressor. Such sucking in of additional air to the cylinder of the air compressor is shown at -atmospheric pressure from point I to point J which corresponds to the bottom dead center position of the piston of the compressor. It will be noted that point D whereat the plunger 4 reverses its travel occurs at the outward limit of the suction stroke Iof the compressor. It, of course, is to be realized that in certain instances the suction pressure within the compressing cylinder may drop slightly below latmospheric pressure. As is well known a compressor is only capable of compressing air during its compression stroke; however, in the event that cylinder unloader 7 holds the suction valve 9 open during the compression stroke the pressure within the compression chamber normally does not rise above atmospheric pressure. With the suction valve 9 held open the piston of the compressor will merely displace the air charge outwardly of the compression cylinder during the compression stroke for so long as the unloader 7 holds the suction valve 9 open. Under partial load conditions as previously described the point L corresponds to the point E of the control pressure diagram and U of the unloader liftl diagram whereat the unloaders are closed and for a portion (L -M) of the remainder of the compression stroke (If-K) the piston of the compressor compresses the air therein along a generally atabatic line to the point M at which time the discharge valves of the compressor open to permit discharge of compressed air which will occur between the points M--H which represent the remaining portion of the compression stroke of the compressor. In the event that the unloader 7 holds the suction valve 9 in the open position for an idle load condition it will be noted that the point L becomes L and corresponds to the point E of the control system so that air is compressed along the line L-H and no discharge thereof occurs.

From this description of a preferred embodiment of my invention it will be noted that I have provided a control formed from inexpensive components which permits a compressor to run continuously under varying load conditions. Of great importance is the fact that as the compressed medium delivered varies with the amount of compressed medium used, that is the drop in receiver pressure, my control permits the compressor to deliver only the actual amount of compressed medium required. ln addition such varying amounts of compressed medium may be supplied without requiring any accumulations for maintaining pressure on the unloader or safety valve for preventing any excess pressure from building up in the entire system. Also, due to the rapid breakdown of pressure in my control the unloader is always closed rapidly. Also, although l have described my invention with relation to a hydraulically operated unloader it is to be realized that other hydraulic devices may be employed to operate the hydraulic unloaders. Although I have described a single control which operates to control a single unloader and suction valve such a control may readily be connected to control a plurality of unloaders. In addition more than one of such controls may be provided on a multiple cylinder compressor whereby each cylinder may be so controlled.

Having described a preferred embodiment of my invent in accordance with the patent statutes, it is to be realized that modifications thereof may be made without departing from the broad spirit and scope of my invention. Accordingly, it is respectfully requested that my invention be interpreted as broadly as possible and as limited only by the prior art.

What I claim is:

l. Control apparatus for a machine comprising, a housing having an elongated plunger reciprocably mounted therein to obtain periodic increase and release of pressure in a hydraulic uid located in a portion of said housing, a pair of hydraulic passageways connected at one end to said portion of said housing and at the other end to a common passageway, one of said pair of passageways having means therein whereby said one passageway is open when high pressures exist in said portion of said housing and closed when low pressures exist in said portion of said housing, a third hydraulic passagel way connecting the other of said pair of passageways to the outer surface of said plunger at a location longitudinally spaced from said tirst mentioned portion of said housing, said other passageway having means therein to close communication between said other passageway and said third passageway and to close the portion of said other passageway between said portion of said housing and said third passageway, said last mentioned means being movable to connect said third passageway to said other passageway when a higher pressure exists in said common passageway than exists in said portion of said housing, and means on said plunger for connecting said third hydraulic passageway to a low pressure reservoir only after the pressure has started to be released in said portion of said housing.

2. Control apparatus for a machine having a housing having an elongated closed end bore in which `a plunger is reciprocably mounted, a low pressure reservoir connected to said bore at a location spaced from said closed end, said plunger having a head portion closely received within said bore which moves inwardly toward land out= wardly away from said closed end to periodically create and release a high pressure in a medium in the portion of said bore adjacent said closed end, a iirst passageway connecting said reservoir to said bore at a location spaced longitudinally outwardly of said adjacent portion of said bore, a normally closed second passageway having one end terminating on the running surface of said bore, means on said plunger spaced outwardly `from said head portion for connecting said first and second passageways together during an increment of its reciprocable movement, and means operable upon a decrease in pressure in said adjacent portion of said bore for opening said second passageway.

3. Control apparatus for a machine having a housing having an elongated closed end bore in which an elongated plunger is reciprocably mounted, a low pressure reservoir connected to said `bore at a location spaced longitudinally from said closed end, said plunger having a head portion closely received within said bore which moves inwardly toward and outwardly away lfrom said closed end to periodically create and release a high pressure in a medium in the portion of said bore adjacent said closed end, a iirst passageway connecting said reservoir to said bore at a location spaced longitudinally outwardly of said adjacent portion of said bore, a second passageway having one end terminating at said bore, control means on said plunger spaced outwardly from said head portion for connecting said iirst and second passageways together during an increment of its reciprocable movement, means operable upon a decrease in pressure in said adjacent portion of said bore for opening said second passageway and said control means being of a configuration so that rotation of said plunger about its longitudinal axis varies said increment.

4. Control apparatus comprising, a housing having a chamber therein, means movable in one manner for creating a high pressure in a medium in said chamber and movable in another manner to release the pressure in such a medium, a pair of passageways communicable with each other, one of said passageways being connected to said chamber to receive such a high pressure mediumtherefrom, valve means yfor normally preventing communication between said passageways, said valve means opening communication between said passageways only when said movable means is moving in said other manner, and means on said movable means cooperable with the other of said passageways after movement of said movable means in said other manner has been initiated for rapidly releasing high pressure throughout said passageways.

5. Control apparatus comprising, a housing having a chamber therein, means movable in one manner for creating a high pressure in a lmedium in said chamber and movable in another manner to release the pressure in such a medium, a pair of passageways communicable with each other, one of said passageways being connected to said chamber to receive such a high pressure medium therefrom, valve means for normally preventing communication lbetween said passageways, said valve means being operable in response to decreasing pressures in said chamber =to open communication between said passageways, and means on said movable means cooperable with the other of said passageways after movement of said movable means in said other manner has been initiated for rapidly releasing high pressure throughout said passageways.

6, Control apparatus comprising, a housing having a chamber therein, a plunger linearly movable in one direction for creating a high pressure in a medium in said chamber, said plunger being linearly movable in a direction opposite said one direction to cause the pressure of said medium to decrease, a pair of passageways communicable with each other, one of said passageways being connected to said chamber to receive such a high pressure medium therefrom, valve means Vfor normally preventing communication between said passageways, said valve means opening communication between said passageways only when said plunger is moving in said opposite direction, and means on said plunger cooperable with Ithe other of said passageways after movement of said plunger in said opposite direction has been initiated for rapidly releasing high pressure throughout said passageways.

7. Control apparatus comprising, a housing having an elongated bore therein, an elongated plunger movable in said bore towards and away from one end thereof for creating and releasing a high pressure in a medium in said one end thereof, a pair of passageways communicable with each other, Vone of said passageways being connected to said one end of said bore to receive such a high pressure medium therefrom, valve means for normally preventing communication between said passageways, said valve means operable upon a decrease in pressure in said one end of said bore to open communication between said passageways, the other of said passageways extending through at least a portion of said housing with the end thereof remote from the end controlled by said valve means terminating in the running surface of said bore remote from said one end thereof, and means on said plunger remote from said one end of said bore cooperable with said remote end of said other passageway after such pressure release in said one end of said bore has been initiated for rapidly releasing high pressure throughout said passageways.

8. Controlrapparatus comprising, a housing having a chamber therein, means selectively movable in said chamber for creating and releasing a high pressure in a medium in said chamber, a pair of passageways communicable with each other, one of said passageways being connected to said chamber to receive and retain such a high pressure medium therefrom, valve means for normally preventing communication between said passageways, said valve means being connected to said chamber to open communication between said passageways only when the pressure in said chamber is decreasing, and means on said movable means selectively operable and cooperabie with a separate passageway that communicates with the other of said passageways after said chamber pressure decrease has been initiated for rapidly releasing high pressure throughout said passageways.

9. Control apparatus comprising, a housing having a chamber therein, means movable in one manner for creating a high pressure in a medium-in said chamber and movable in another manner to release the pressure in such a medium, a pair of passageways communicable with each other, one of said passageways being connected to said chamber to receive such a high pressure medium therefrom, valve means for normally preventing communication `between said passageways, said valve means operable upon a decrease in pressure in said chamber to open connnunication between said passageways, means on said movable means cooperable with the other of said passageways after movement of said movable means in said other manner has been initiated for rapidly releasing high pressure throughout said passageways, and said movable means also being movable in still another manner to vary the instant said 'other passageway cooperates with said means on said movable means with reference to movement of said movable means in said first mentioned other manner.

l0. Control apparatus comprising, a housing having a chamber therein, means selectively movable in said chamber for creating and Ireleasing a high pressure in a medium in said chamber, a pair of passageways communicable with each other, one of said passageways being connected to said chamber to receive and retain such a high pressure medium therefrom, valve means for normally preventing communication between said passageways, said valve `means having spaced portions upon which the pressures of such a medium in said one passageway and said chamber are exerted respectively, said valve means opening it?, communication between said passageways only when the pressure of such a medium in said one passageway produces a force on said valve which is suicient to overcome the force exerted on said valve by such a medium in said chamber, and means on said movable means cooperable with the other of said passageways `through a separate passageway after said chamber pressure decrease has been initiated for rapidly releasing high pressure throughout -said passageways through said separate passageway.

ll. Control apparatus comprising, a housing having a chamber therein, means movable in one manner for creating a high pressure in a medium in a portion of said chamber and movable in another manner to release the pressure in such a medium, said housing having a low pressure reservoir connected to said chamber, a pair of passageways communicable with each other, one of said passageways being connected to said chamber to receive such a high pressure medium therefrom, valve means for normally preventing communication between said passageways, said valve means opening communication between said passageways only when said movable means is moving in said other manner, and means on said movable means cooperable with the other of said passageways after movement of said movable means in said other manner has been initiated to connect said other of said passageways to said reservoir whereby a rapid release of high pressure occurs throughout said passageways.

l2. Control apparatus comprising, a housing having an velongated bore therein, an elongated plunger movable in said bore towards and away from one end thereof for creating and releasing a high pressure in a'mediurn in said one end thereof, said housing having a low pressure reservoir connected to said bore outwardly from said one end, a pair of passagewayscommunicable with each other,

one of said passageways being connected to said one end of said bore to receive such a high pressure medium therefrom, valve means for normally preventing communica- Vtion between said passageways, said valve meansoperable upon a decrease in pressure in said one end of said bore to open communication between said passageways, the other of said passageways extending through at least a portion of said housing with the end thereof remote from the end controlled by said valve means terminating in the running surface of said bore remote from said one end thereof, and means on said plunger remote from said one end of said bore cooperable with said remote end of said other passageway after such pressure release in said one end of said bore has been initiated to connect said other passageway to said reservoir whereby a rapid release of high pressure occurs throughout said passageways.

15.'Control apparatus comprising, a housing having a chamber therein, means movable in one manner for creating a high pressure in a medium in said chamber and movable in another manner to release the pressure in such a medium, a passageway connected to said chamber to receive a high pressure medium therefrom, and means in said housing cooperable with means on said movable means for rapidly releasing high pressure medium from said passageway after movement of said movable means in said other manner has occurred.

14. Control apparat-us comprising, a control device having means actuated by a pressurized medium, a pump having discharge controlling means connected to said means of said control device, said pump having a chamber in which a medium is pressurized which pressure is subsequently released, said discharge controlling means being connected to said chamber to receive pressurized medium therefrom, and said ptu'np having means connected by a separate passageway to said discharge controlling means for selectively releasing pressurized medium therefrom after the pressure has been released in said chamber and vindependently of length of time of pressure collapse in said chamber.

l5. Control apparatus comprising, a control device having means actuated by a pressurized medium, a pump having a housing with a chamber therein, said pump having means movable in one manner for creating a high pressure in a medium in said chamber and movable in another manner to release the pressure in such a medium, a pair of passageways communicable with each other, one of said passageways being connected to said chamber to receive such a high pressure medium therefrom, said one passageway being connected to said means of said control device, valve means for normally preventing communication between said passageways, said valve means opening communication between said passageways only when said movable means is moving in said other manner, and means on said movable means cooperable with the other of said passageways after movement of said movable means in said other manner has been initiated for rapidly releasing high pressure throughout said passageways 16. Control apparatus comprising, a control device having means actuated by a pressurized medium, a pump having a housing with a chamber therein, said pump Ihaving means movable in one manner for creating a high pressure in a medium in a portion of said chamber and movable in another manner to release the pressure in such a medium, said housing having a low pressure reservoir connected t0 said chamber, a pair of passageways communicable with each other, one of said passageways being connected to said chamber to receive ysuch a high pressure medium therefrom, said one passageway being connected to said means of said control device, valve means for normally preventing communication between said passageways, said valve means opening communication between said passageways only when said movable means is moving in `said other manner, and means on said movable means cooperable with the other of said passageways after movement of said movable means in said other manner has been initiated for rapidly releasing high pressure throughout said passageways.

References Cited in the tile of this patent UNITED STATES PATENTS 1,596,194 Lang Aug, 17, 1926 2,090,781 Camner Aug. 24, 1937 2,247,421 Tabb et al. July 1, 1941 20 2,582,896 Acton Ian. 15, 1952 2,605,141 'Pyk et al July 29, 1952 FOREIGN PATENTS 59,555 France Feb. 3, 1954 

